LOW-RATE DYNAMIC CONTACT ANGLES ON POLYSTYRENE AND THE DETERMINATION OF SOLID-SURFACE TENSIONS

Low-rate dynamic contact angles of 13 liquids on a polystyrene polymer are measured by an automated axisymmetric drop shape analysis - profi le (ADSA-P). It is found that 7 liquids yielded non-constant contact a ngles, and/or dissolved the polymer on contact. From the experimental contact angles of the other 6 liquids, it is found that the liquid-vap or surface tension times cosine of the contact angle changes smoothly with the liquid-vapor surface tension, i.e. gamma(lv)cos theta depends only on gamma(lv) for a given solid surface (or solid surface tension ). This contact angle pattern is in harmony with those from other iner t and non-inert (polar and non-polar) surfaces (7-13, 24-26). The soli d-vapor surface tension calculated from the equation-of-state approach for solid-liquid interfacial tensions (33) is found to be 29.8 mJ/m(2 ), with a 95% confidence limit of +/-0.5 mJ/m(2) from the experimental contact angles of 6 liquids.